This disclosure pertains to optical imagers in general and in particular to a high speed optical imager having a wide field of view.
Demand for imaging sensors that provide wide area persistent surveillance is increasing. Wide area persistent surveillance often requires high resolution imagery over a large area. However, current infrared imagers or image sensors merely provide large area coverage or provide high resolution but do not provide both a large area coverage and high resolution. In addition, long wavelength infrared (LWIR) imagers require fast f-numbers (i.e., small f-numbers) to produce valuable imagery. Hence, designing a LWIR optical system that combines both large area coverage and high resolution can be challenging. At the present time there are no known imaging system that can provide imaging in the LWIR range (between about 8 μm and about 12 μm) while at the same time provide large area coverage and high resolution imagery.
Conventional systems or methods for providing large or wide area coverage and high resolution imagery rely on (a) stepping or scanning a small, high resolution, field of view (FOV) relatively quickly over the coverage area, or (b) using a switchable FOV where a low resolution wide field of view (WFOV) used to cover the wide area is switched to a narrow field of view (NFOV) to provide a high resolution image of a sub-region of interest within the wide area.
Both of the above configurations (a) and (b) have certain limitations in that they do not provide continuous high resolution data or imagery. In other words, imaging of the entire area is not captured simultaneously. Therefore, some image information within the wide area may be missed, not captured or fully captured during stepping and scanning, in the case of (a), or during zooming to a sub-region of interest within the wide area, in the case of (b). In addition to these limitations, both of these configurations involve adding mechanisms which can be costly and may have reliability concerns.
Therefore, there is a need in the art for optical imagers having a fast f-number that can provide a wide field of view (WFOV) and relatively high resolution in the LWIR range. In this context, a “wide” FOV may be considered, by way of a non-limiting example, to be greater than 20 degrees (for example greater than 40 degrees), and a fast f-number may correspond to an f-number less than about F/2.